Such measuring systems have been known from various publications and are suitable, depending on the wavelength range used, for measuring the concentrations of gases, e.g., for the measurement of CO.sub.2 or also for determining the concentration of alcohol in the exhaled air of a human.
A measuring device of this class is described in DE 195 20 488 C1, in which the gas to be measured flows by diffusion into the hollow guide used as the measuring path.
A multispectral sensor for the infrared range has become known from DE 41 33 481 C2 corresponding to U.S. Pat. No. 5,300,778, in which different spectral ranges of a radiation to be measured are detected by separate detectors, wherein a compact design with high measuring sensitivity and accuracy is said to be possible.